Fixed wing aircraft are exemplified in civil aviation by modern passenger transport aircraft, such as the various aircraft models manufactured by Airbus and Boeing. Such fixed wing aircraft typically include slats movably arranged along the leading edge of each wing, and flaps movably arranged along the trailing edge of each wing. By selectively extending and retracting, and/or selectively deflecting, such flaps and/or slats, the aerodynamic flow conditions on the respective wing are influenced so as to increase the lift generated by the wing, for example especially for take-off and landing phases of flight of the aircraft. In general, such flaps and slats are known as lift-enhancing devices, which can also be categorized as take-off aids or landing aids. These lift-enhancing devices taken collectively form the flap system of the aircraft, which is monitored and also regulated with respect to the flight situation or configuration by a flight control arrangement of the aircraft, for example in order to carry out a take-off and/or landing on an airport runway in an optimal manner. In this regard, the actual current flight data of the aircraft are continuously provided to the aircraft flight control arrangement, which in turn regulates the actuation of the components of the flap system in a manner depending on the particular flight situation at hand, in order to vary the camber of the lifting wing profile, to vary the lifting wing surface area, and/or to influence the boundary layer so as to adjust the lift and drag characteristics of the wing as required.
Conventional flap systems typically include a central drive motor, drive transmission stations of the leading edge slats and of the trailing edge flaps, and a continuous through-going transmission shaft that forms a centralized shaft line which transmits the drive power from the central drive motor to the several drive stations. A typical example of such a conventional arrangement is shown in FIG. 1, which relates to the landing flap system of the Airbus A340 aircraft. A monitoring system carries out a continuous monitoring of the shaft line. In this regard, in each lifting wing, a safety brake and a monitoring sensor are mechanically coupled to the shaft. A further safety brake and a monitoring sensor are integrated in the central drive, where by the sensors serve to detect deviating position differences or asymmetries and overspeed conditions. In the event the transmission shaft breaks, only those flaps that remain mechanically coupled to the central drive via the remaining functional portion of the transmission shaft would remain controllable, while the other flaps could no longer be controlled with regard to their respective positions and aerodynamic influences. Such a lack of control could have catastrophic consequences for the overall control and flight safety of the aircraft.
Furthermore, such conventional flap systems including a central drive and a rather long continuous transmission shaft necessitate a rather high installation effort and expense, because the transmission shaft for the flaps or slats respectively must be laid out to run along the trailing edge or the leading edge of the wing. Particularly also, the transmission shaft must be guided or laid out in such a manner to turn through several corners or angles as it transitions from the wing into the fuselage, and then extends transversely through the fuselage. This layout of a continuous transmission shaft in connection with a central drive also results in a relatively high friction exerted on the rotating shaft, and thus a relatively high required drive power already for overcoming the friction, which in turn results in a rather poor operating efficiency. Furthermore, it is necessary to consider the dynamics of the transmission shaft line represented by the rotational spring-mass-damping characteristics.
Moreover, such a continuous transmission shaft necessarily provides a positive fixed mechanical synchronization of all of the flaps or slats connected to the respective shaft. This allows a synchronization of the flaps between the left and right lifting wing to be realized, for controlling or dealing with asymmetrical flap deflections. As is known, an excessive asymmetrical flap deflection of the flap system can lead to critical flight conditions, which are no longer controllable.
In addition to the above described single shaft line systems, solutions having two shaft lines are also known, for reasons of redundancy. However, in such systems, the flaps or slats of the left wing and of the right wing are mechanically coupled with each other. Such a conventional system is generally shown in FIG. 2, which exemplifies the landing flap system of the Boeing B747 aircraft. In that system, the inboard flaps and the outboard flaps are respectively mechanically coupled via a shaft with a respective drive, and are thereby synchronized with one another.
Furthermore, with reference to the example of the DC9 and DC10 aircraft, it is also conventionally known to provide a flap system in which the flaps arranged on the lifting wing are respectively connected to and driven by individual drives. However, these individual drives are hydromechanically coupled with each other and thereby synchronized in a relatively complex manner. In this regard, two hydraulic cylinders are utilized for moving each respective flap, whereby each individual drive is connected to a common hydraulic system. For this reason, it is not possible to enhance or expand the available functionality of the flap system. Namely, such flap systems have the disadvantage that only a simple or singular flap kinematics can be realized using such a local drive consisting of hydraulic cylinders. Due to the hydraulic coupling of the several drives, an individual deflection or extension/retraction of a single flap is not possible, because all of the drives of all of the flaps are connected to the same hydraulic control valve. A further disadvantage of such a hydraulically coupled system, which is not shown herein, is that any malfunctions or faults in the flap system arising during flight of the aircraft cannot or essentially not be localized, and a relatively time-consuming manual search for the fault site will be necessary while the aircraft undergoes maintenance and service on the ground.